Shoppers from every financial stratum are stalking Art Basel, which the New York Times is characterizing as among "the most glamorous doorbuster sales in history."

But the man from the very apex of the art food chain is glaringly missing. Hedge fund billionaire Steven A. Cohen has not been seen and the sinking feeling in the pit of many a gallery owner's stomach is that legal issues related to a supposed insider trading scheme at Cohen's own firm may have sidelined one of art's richest and most reliable collectors.

The real person of interest in the trading case at SAC Capital Investors is Matthew Martoma and it’s not clear if Cohen is in real legal danger. But if he is, gallery owners are telling the Times, it will be very bad news.

As a general rule, the more business they have conducted with the man, the more worried they are likely to be.

“It’s disconcerting,” said Timothy Blum, co-owner of Blum & Poe, a gallery in Los Angeles. “We’re talking about a lot of liquid,” he added, meaning money. “A lot of liquid. I’ve never calculated it out, but he’s responsible for a significant percent of our business.”

For Mr. Blum and other elite gallery owners, there is sincere dread at the notion, however remote, that Mr. Cohen may one day be sidelined. Known in the securities world for astounding investment returns and an occasionally volcanic temper, he is described by dealers as the ideal collector — warm, dedicated, eager to take home the best pieces and unafraid to spend what it takes.

“We would absolutely hate to have him not active in the market, I can wholeheartedly say that,” said David Zwirner, who owns a gallery that bears his name in the Chelsea section of Manhattan. “This man is a friend of mine. I called him last week — ‘How are you? What’s going on?’ I think the art world is rooting for him. I’m rooting for him. I wish he were here right now.”

What's on Cohen's walls already? Works by Jackson Pollock, Andy Warhol, Damien Hirst and Édouard Manet among many others. Experts say Cohen has so much money, he would probably never have to sell any of his collection and, even if he did, the stain of a prosecution for financial wrongdoing would be unlikely to affect the value.

Burt even if Cohen were to go to prison, insiders say, there are many other billionaires standing by to pick up the slack.